Today is February 29, leap day .  Why do we have this?   Through the course of a whole year, to keep our season stable, you would need to add nearly 6 hours.   In other words, over the course of 120 years, the world would gain a month, and if this continued, agriculture, for one, would be affected. So you make this up every four years.   Actually, the gain is 5 hours, 48 minutes and 20 seconds. Note that the world skipped leap years in 1700, 1800 and 1900, but not 2000.  The next leap year to be skipped will be in 2100. Leap year was recognized by the Egyptians more than 5000 years ago, but it took them 2700 years to establish a new calendar. In time Hebrew, Chinese and Buddhist time-keepers added a full month every 120 years. However, Rome in 46 BC, then ruled by  Julius  Caesar, added an extra day at the end of February every four years, which for them was the last month of the year.  Thus the  Julian  Calendar. Pope  Gregory  XIII in 1586 decreed that 10 days be skipped, creating